The invention relates to a method for processing a sensor signal of a knocking sensor for an internal combustion engine.
In internal combustion engines with spark ignition (spark ignition engines), the fuel mixture in the combustion chambers of the internal combustion engine can partially ignite automatically as a result of the compression of the internal combustion engine, which leads to what is referred to as knocking and is manifest, for example, in the form of undesired vibrations.
It is therefore known to monitor the knocking behavior of internal combustion engines with spark ignition so that the engine control can, if appropriate, be counteracted appropriately. For this purpose, it is known to use knocking sensors for example in the form of vibration sensors or pressure sensors which supply a knocking signal whose evaluation allows the knocking behavior of the internal combustion engine to be determined. When the sensor signal is evaluated, only a specific time window of the sensor signal is considered, the position of said time window corresponding to a specific angular position of the crankshaft of the internal combustion engine, the sensor signal containing, within this time window, particularly revealing information on the knocking behavior of the internal combustion engine. The sensor signal which is registered during this time window is then subjected to bandpass filtering, the center frequency of the bandpass filtering being set in such a way that the frequency range of the knocking signal lies within the transmission range of the bandpass filter. The signal energy of the bandpass-filtered knocking signal is then calculated during the predefined time window, which can be done by integrating the squared signal. The knocking signal which is prepared in this way then makes it possible to determine the knocking behavior using the engine electronic system so that the engine electronic system can correspondingly counteract knocking when it occurs.
A disadvantage with the known signal processing method described above is the relatively complicated processing during the bandpass filtering and the calculation of the signal energy. The application of the known signal processing method therefore requires relatively complex hardware and a relatively large amount of computing time.
DE 690 17 063 T2 also discloses a method for evaluating a knocking signal in which the knocking signal is sampled with a predefined sampling rate and subsequently subjected to a Fourier transformation. The sampling rate is set here in accordance with the current state of the engine in order to permit the best possible detection of knocking.
However, a disadvantage with this method is that the relationship between the state of the engine and the resulting sampling rate is permanently predefined in an engine-specific fashion. Without complex adaptations this method is suitable only for a specific type of engine.
In addition, DE 42 23 649 C2, DE 691 05 256 T2, DE 690 05 256 T2, DE 100 22 815 A1 and DE 195 20 033 A1 have disclosed a method and/or device for evaluating or synthesizing knocking signals in which the knocking signal is sampled and subsequently subjected to a Fourier transformation.
However, without complex adaptation these known methods are also only suitable for a certain type of engine.